System of electrical distribution.



No. 7I0,082. Patented Sept. 30', I902. c. P. STEINMETZ &. L. R. EMMET.

SYSTEM OF ELECTRICAL DISTRIBUTION.

(Application filed m). 1:, 1902.

(In Model.)

'4 Inventors CharlesFlSGemrneGz CUilIiamLeRo Emmet 5 I I F by away CDHSnesses:

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UNITED STATES PATENT CEEICE.

CIIARLES P. STEINMETZ AND WILLIAM L. R. EMMET, OF SCHENECTADY,

NEW YORK, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPO- RATION OF NEW YORK.

SYSTEM OF ELECTRICAL DISTRIBUTION.

SPECIFICATION forming part of Letters Patent No. 710,082, dated September 30, 1902.

Original application filed December 21, 1899, Serial No. 741,101. Divided and this application filed February 13, 1902.

Serial No. 93,832. (No modeLl To all whom, it may concern.-

Be it known that we, CHAELEs P. STEIN- METZ and WILLIAM LE. R. EMMET, citizens of the United States, residing at Schenectady, county of Schenectady, State of New York,

have invented certain new and useful Improvements in Systems of Electrical Distribu- --tion, (Case No. 2,716, division of Serial No. 741101, filed December 21, 1899,) of which the following is a specification.

Ourpresentinvention relates to alternatingcurrent systems of distribution, and as to some of its features more especiallyto that arrangement in which a neutral conductor is brought out from a point of neutral potential on an alternating-current-supply system and is led forward and cooperates with direct-current mains of a converter to form a multipleconductor direct-current system of distribution. There a system of transformers is used for feeding the converter, the invention is particularly valuable in that it permits a reduction in the number of transformers which has heretofore been found necessary for feeding a converter of any given number of phases.

In the embodiment which we have selected for the purpose of illustrating our invention the alternating current from the source is passed through a system of phase-changing transformers, the currents from the secondaries of which are suitably proportioned and passed to the armature of the converter, by which they are changed into direct current.

The scope of our invention will be better understood, both as to its broad features and in its more limited details, by reference to the claims appended hereto, while a better understanding of the same, both in its construction and mode of application, will be had by an examination of the following description, taken in connection with the accompanying drawing, in which- Figure 1 represents one form of our invention in diagram; Fig. 2, an explanatory diagram, and Fig. 3 a modification.

One of the features of our invention consists in supplying a rotary converter having a number of phases represented by a multiple of three by currents which are the resultants of currents displaced from each other in phase by ninety degrees. In the instance shown a six-phase'rotary converter is fed by means of two overlapping T-connected threephase systems, the nature of which will be best understood by reference in detail to the drawings. Fig. 1 represents such a system, and Fig. 2 denotes the relation of electromotive forces operating therein.

Referring first to Fig. 2, the dotted circle represents the locus of the ends of vector electromotive forces combined to produce a six-phase system. The particular relation of electromotive forces chosen consists of two sets of quarter-phase electromotive forces, each set consisting of an electromotive force of given value Operating in conjunction with another electromotive force having a'ratio thereto of g, the electromotive forces being so combined that the resultant electromotive forces represented by connecting the ends of the vectors will be equal. Thus theline 1 may represent one ofthese electromotive forces or vectors and the line 2 the other, displaced from 7 E the first by ninety degrees and combined with the first electromotive force 1, so that the end of the vector 2 is connected to the middle point in the length of the vector 1. With the proportions indicated the resultant vector formed by connecting either end of the vector 1 with the free end'of the vector 2 is equal to the vector 1. Such a system of electromotive forces is produced in practice by the use of two transformer or other windings carrying currents in quarter-phase relation to each other and connected so that the end of one winding joins the middle point in the other winding, the electromotive forces of'the windingsbeing suitably proportioned, as before referred to.

A second system of electromotive forces is indicated in Fig. 2 by the lines 3 4; but these electromotive forces operate in a reverse relation with respect to the first set, as will be 5 seen. The inscribing circle is thus divided into siX equal parts by means of the intersections of the lines 1 to 4, these intersections representing the points of connections of windings carrying electromotive forces related to each other and arranged in the proportions indicated. The physical embodiment of such a system is diagrammatically shown in Fig. 1, in which the winding 11 represents a winding generating an electromotive force corresponding to the line 1 of Fig. 2, while the winding 22, connected at one end to the middle of the winding 11, represents the line 2 similarly connected to line 1. In a similar manner the winding 33 corresponds to the line or electromotive force 3 shown in Fig. 2, while the winding 44 corresponds to the line 4 connected to the middle point of the line 3. It is to be noted that while the lower end of the line 4 is connected to the middle point of the line 3, the upper end of the line 2, on the contrary, is similarly connected to the middle point of the line 1. The connections of these lines being reversed the connection of the winding 44 is accordingly reversely connected with the Winding 33 in order to reproduce the arrangement of electromotive forces indicated in Fig. 2. This is shown in the drawing by connecting the left-hand end of the winding 22 to winding 11, while, on the contrary, the right-hand end of the winding ll: is connected to the winding 33. If the terminals of these windings be connected to equally-spaced points in a closed armature-winding, according to the scheme of connections represented in Fig. 2, then resultant six-phase currents will fiow in said armature-winding.

AtOisindicated the armature-winding of a rotary converteigfrom which taps are brought out at six equally-spaced points and connected to suitable collector-rings. These rings are connected to the supply system in the following manner: The rings 5 6 lead to the terminals of the winding 11 and are connected to points in the armature displaced from each other by one-third of the polar pitch. In a similar manner the rings 7 8 receive current from the ends of the winding 33 and are connected across the same arc in the armaturewinding as the rings 5 and 6, the connections being made in such a manner that the middle of thearc formed by the connection of the rings 7 and 8 is displaced one-half of the polar pitch from the middle point of the are formed by the connection of the rings 5 and 6. Since the windings 11 and 33 are inductively related to the same primary excitingwinding 9, they give rise to electromotive forces in the same phase, and their sphere of action is represented in Fig. 2 by the lines of electromotive force 1 and 3.

The collector-ring 10 leads from a point in the armature-winding of the converter midwaybetween the connection ofthe rings 5 and 6 and receives current from the free end of the winding 44:, the other end of which is connected to the middle of the coil 33, as previously described. In a similar manner the ring 11' leads from a point in the armaturewinding midway between the points of connection of the rings 7and 8 and receives current from the free end of the winding 22, the opposite end of which is connected to the middle of the'winding 11, as already mentioned. The arrangement shown corresponds to a bipolar field, so that if the field is multipolar the connections are to be made accordingly, as will readily be understood. With the system of connections thus described the quarter-phase electromotive forces circulating in the windings of the supply system are so combined when they reach the converter-armature as to produce therein six-phase currents,

the use of a smaller number of transformers than has hitherto been found necessary it at the same time affords an easy means for obtaining a point of neutral potential, to which a neutral conductor from the threewire system may be connected in a well-understood manner. Thus, as seen from Fig. 2, the center of the circle constituting the 10- cus of the ends of lines representing electromotive forces lies within both of the lines 2 and 4, which actually are superposed on each other, but which for convenience of illustration are shown in the figure as parallel to each other and slightly separated. From the geometry of the figure it will be seen that this point lies two-thirds of the distance from the outer end of each of the lines 2 and 4. Since the windings 22 and 44 represent sources of electromotive force related in the same way as the lines 2 4, this point of neutral potential may be obtained by connecting together points in the said windings located twothirds of the distance from the free ends of the respective coils. The point 14 is accordingly connected with the point 15, thus making the common connection a point of neutral potential with respect to the resultant electromotive forces existing at the collectorrings of the converter. The neutral conductor 0 leads from this common connection and cooperates with the direct-current mains 12 and 13 to form a three-wire distributing system.

In some cases there may be considerable practical difficulty in connecting intermediate points in the transformer-windings in order secure a neutral, particularly so where the transformers are not specially constructed or particularly desirable, since while permitting their coils easily accessible. In such cases we make use of the following device: The tapping-in points 16 and 26 of the T-connected windings are joined by means of a compensator, to the middle point in the length of which the neutral conductor is connected.

In Fig. 3 so much of the system in Fig. 1 is shown as is necessary to understand the connections of the compensator. Thus in Fig.3 the coils 11 and 33 are the same as the coils 11 and 33 in Fig. 1, while the leads 17 and 18 are supposed to be connected to cooperating coils in exactly the same manner as the leads 17 and 18 in Fig. 1. The only differenceis that the neutral conductor 0 (shown in Fig. 1) is in this case not connected to the points 1e and 15, but, on the contrary, to the middle point of the compensator L, (shown in Fig. 3,) the terminals of the compensator being connected, respectively, to the middle points of the windings 11 and 33.

Throughout the above description we have purposely refrained from stating in what manner the secondary windings of the alternating-supplysystem were to receive current from the source of supply. It is to be understood, however, that this connection is to be made in such a manner as will cause quarterphase electromotive forces to be set up in the windings in direct connection to the converter. For this purpose these windings may be supplied by means of quarter-phase primary windings, or if currents of this phase relation be not employed then by other currents combined in such a manner as to produce resultant quarter-phase fluxes arranged to act upon said windings inductively or otherwise.

In Fig. 1 we have shown three-phase mains a b c, feeding the two primary windings 9 9. These primary windings, however, are connected with the end of one to the middle point of the other and are so proportioned that the winding constituting the base is related to the other in the proportion of 2: V3, whereby when three-phase currents are fed to the three free terminals of the windings as thus connected resultant quarter-phase currents are produced, which latter act to set up similarlyrelated electromotive forces in coils inductively related thereto. It will thus be seen that the primary 9 and its free end, in conjunction with the free ends of the primary 9, receiving current from three-phase mains, operates to set up quarter-phase electromotive forces in the secondary windings heretofore referred to.

Although for the purpose of making clear the nature of our invention we have described a particular and specific embodiment of the same, it is to be understood that we are not to be limited to the details of the invention thus described, but that, on the contrary, our claims are to be given a much broader scope. Thus as a concrete example the converter heretofore mentioned need not necessarily be supplied with current from transformers, but may instead receive current from suitable windings on dynamo-electric generators or the like. 1

\Vhat we claim as new, and desire to secure by Letters Patent of the United States, is

1. The method which consists in deriving quarter-phase electromotive forces by the action of three-phase currents, combining said electromotive forces in proper proportions to produce resultant sixphase electromotive forces, and deriving direct current from said six-phase electromotive forces.

2. The method which consists in setting up quarter-phase electromotive forces, combining said electromotive forces in such relations and in such proportions as to produce sixphase electromotive forces and deriving direct current from said six-phase electromotive forces.

3. The method which consists in setting up quarter-phase electromotive forces, combining said electromotive forces in such relations and in such proportions as to produce a system of polyphase electromotive forces having a number of phases greater than two and deriving direct current from said system of electromotive forces.

In witness whereof we have hereunto set our hands this 11th day of February, 1902.

CHARLES P. STEINMETZ. WILLIAM L. R. EMMET.

Witnesses:

BENJAMIN B. HULL, MARGARET E. WooLLnY. 

